With broad match the Google Adwords system automatomatically runs your ads on relevant variations of your keywords, even if these terms aren't in yur keyword list. This feature is known as expanded broad match. Keyword variations can includ synonyms , singular/ plural forms, relevant variations of your keywords and phrases containing your keywords.

To find out how to see which terms your ads are actually being shown for, you will need to run a search query performance report. This report has only recently been added to the Google AdWords system.

Sounds like it's worth testing how broad it actually is. could be helpful for finding new terms.

The results will be very different depending on the language, I suppose. In Russian it won't give all possible options:

I tried it today. All it gives you is: Search Query,Search Query Match Type, Impressions,Clicks,CTR,Avg CPC,Cost,Avg Position, of all already existing keywords in you're campaign (you can choose the level). Nothing else, no new keywords. Besides, whats the point of adding new found keywords via such a tool, if Google considers them anyway?

The “Search Query Performance Report” could be useful for new terms of both positive and negative match.
It might return search phrases that we did not think of, maybe phrases that only recently occurred in our society, as languages always change. Even though Google matches your keyword, say “holiday”, with synonyms and singular/plural, it is still worth adding them to the campaign aiming to reach more people, not just the ones that type in “holiday”. We could be bidding on those words that don’t enter searchers’ minds at first to attract more people clicking at a lower cost per click, especially once that new keyword has been included in the creative. On the negative side, Google might match too many unwanted keywords, simply because the technique behind it assumes that people searching for “holiday” might mean “relaxation” or something similar. These could then be added as negatives.

I would agree it is good for finding negatives. Have you ever tried this report Sandy?

Yes, I have run the report. For some ad groups you can see the search term that was entered in the search engine. For others you can only see, for example "7 unique entries". This is due to privacy reasons, which Google cannot reveal further at the moment because the report was only recently implemented.